1. Field of the Invention
The present invention relates to a polarized optical article which maintains its integrity after typical processing of an optical article which includes edging. Delamination of the polarizing wafer can be prevented by using a glyoxal adhesive system and process for manufacturing same.
2. The Prior Art
According to the prior art, glyoxal is widely used as a film additive, for example to improve the properties of polyvinyl alcohol (PVA) films. In the Polymer Journal, Vol 25, No. 12, pp 1295-1302 (1993) article entitled Effects of the Degree of Cross Linking on Properties of PVA Membranes, the authors propose using glyoxal and glutaraldehyde as film additives. In the Korean J. of Chem. Eng, 11(1), 41-47(1994) the article states that “to increase the stability of PVA membrane to water, it should be cross linked with an aldehyde”. The article proposes to use glutaraldehyde as the aldehyde of choice. Similarly, U.S. Pat. No. 4,357,402 describes preparing a film and cross-linking with a dialdehyde such as glyoxal or polyaldehydepolysaccharide compounds.
U.S. Pat. No. 5,114,999 discloses using glyoxal as a binder insolubilizer in a paper coating composition. U.S. Pat. No. 5,496,649 mentions that PVA is susceptible to moisture and to decrease its sensitivity one could cross-link using formaldehyde/acid. General cross-linking of PVA using dialdehydes is described in U.S. Pat. No. 4,902,464.
Glyoxal is also used as a crosslinking agent in adhesive formulations, for example, as a crosslinking agent for polyvinyl alcohol (PVOH) adhesive used in PVA and cellulose triacetate (TAC) film lamination. Glyoxal is a well known crosslinking agent within the PVA film industry to improve water resistance. However, there has not been a suggestion to use it as an adhesive to bond PVA polarizing film and TAC film. Furthermore, as taught in U.S. Pat. No. 7,704,572, glyoxal is always used as an additive, for example as a cross-linking agent used in a minor quantity in an adhesive where the adhesive represents the main component of the formulation. Other approaches suggest using metal crosslinking materials (U.S. Published Patent Application 2008/0278810) and other crosslinking agents such as glyoxal (U.S. Published Patent Application 2006/0155061) in PVOH adhesive to improve the film's water resistance. However, tests using these proposed adhesives failed to achieve the minimum requirements for adhesion. Therefore there remains an adhesion problem that needs a solution.
In all of the prior approaches, glyoxal was used as a film additive or crosslinking agent and not as the main adhesive component. It is our desire to improve wet edging and wet adhesion performance in the presence of water. Therefore, it would be desirable to provide an adhesive to form a TAC/PVA/TAC polarizing film ensemble with improved wet adhesion. Furthermore, it would be useful to employ such an adhesive in a polarizing film ensemble laminated to a lens which is then wet edged.